National Geographic Daily News

Trilobite Fossil

Photograph by James L. Amos

Trilobites, like this perfectly preserved specimen at South Dakota's Black Hills Institute of Geological Research, were among the most successful organisms ever to populate Earth. These familiar marine arthropods first arose about 545 million years ago in the early Cambrian and thrived throughout the world's oceans until they were wiped out in the Permian extinctions about 250 million years ago.

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